1. Field of the Invention
The invention relates to the field of communication. More specifically, the invention relates to communication networks.
2. Background of the Invention
The multi-protocol label switching (MPLS) protocol may be categorized as a network layer protocol of the Open Standards Institute (OSI) reference model. MPLS provides a method for generically tunneling data through networks with label switching paths (LSPs).
FIG. 1 (Prior Art) is a diagram of a label stack entry according to multi-protocol label switching (MPLS). A label stack entry 100 is a 32-bit value that includes the following fields: a label identifier field 101, a stack bit field 103, an experimental field 105, and a time to live field 107. The label identifier field 101 includes a 20-bit value identifying a label for a label switch to path (LSP). The stack bit field 103 includes a single bit to indicate whether the label stack entry 100 is the last label stack entry of a packet. The experimental field 105 includes 3 bits reserved for experimental purposes. The time to live field 107 includes 8 bits to indicate the number of hops a label stack entry should exist.
To be used, a label identified by the label identifier field 101 is allocated and then propagated by a label distribution protocol (LDP) module of a label switching router (LSR). The label is passed from the LSR to an upstream LSR for a specific label switched path (LSP) that traverses the upstream LSR and the LSR. If the LSP module of the LSR dies for some reason, the LSR deletes all labels previously allocated for the dead LSP module. In addition, the upstream LSR deletes all forwarding entries with labels learned from the LSR. Since all of the labels propagated by the LSR are deleted, 1) traffic cannot be forwarded along the LSP from the upstream LSR to the LSR and 2) the LSR must allocate another label for the LSP and communicate the newly allocated label to the upstream LSR.